This invention relates to polymeric compositions formed by reacting a hydrophilic monomer, a hydrophobic strengthening agent monomer, a crosslinking agent monomer and a polymerization iniatiator. The novel hydrophobic strengthening agent monomer provides increased strength without decreasing the oxygen permeability of the polymer material.
Soft contact lens materials are made by polymerizing and crosslinking hydrophilic monomers such as 2-hydroxyethylmethyacrylate, N-vinyl-2-pyrrolidone, and combinations thereof. The polymers produced by polymerizing these hydrophilic monomers exhibit significant hydrophilic character themselves, and are capable of absorbing a significant amount of water in their polymeric matrices. Due to their ability to absorb water, these polymers are often referred to as "hydrogels". These hydrogels are optically clear and, due to their high levels of water of hydration, are particularly useful materials for making soft contact lenses. However, the high levels of water of hydration of hydrogels contributes to their relative lack of physical strength which results in hydrogel contact lenses being relatively easy to tear.
Various hydrophobic monomers have been copolymerized with these hydrophilic monomers in order to obtain polymers with improved physical strength. Such hydrophobic monomers include styrene, and various acrylates and methacrylates such as methylmethacrylate, isobornylmethacrylate, and t-butylcyclohexylmethacrylate.
For instance, Chromecek teaches that t-butylcyclohexylmethacrylate is a particularly useful monomer when copolymerized with 2-hydroxyethylmethylacrylate in U.S. Pat. No. 4,436,887. However, while these state of the art hydrophobic monomers do increase the physical strength of hydrogel polymers, they also produce polymers with lower levels of water of hydration than unmodified hydrogels. It is an object of the present invention to provide polymeric materials with increased physical strength and high levels of water of hydration.